In Diesel internal combustion mechanisms, an individual fuel injection means is known as other than concentrated type which is represented by an in-line type and a distributor type. As this type, a unit injector is popular.
In the concentrated type, a pumping mechanism (fuel pressure mechanism) and an injection valve mechanism (injection nozzle) are independent, and on the other hand, the unit injector is characterized in that the injection pumping mechanism and the injection valve mechanism are integrally composed, and they are directly provided to a cylinder head of an engine per each of cylinders.
With respect to the unit injector, in general the injection pumping mechanism and the injection valve mechanism are disposed in series in a housing or a body, but Japanese utility model laid open No. 8827/84 teaches these two mechanisms are disposed transversely each other.
In each of the above embodiments, the injection pumping mechanism is provided with a plunger for receiving transmission of movement from a cam shaft and reciprocating so as to guide sliding of the plunger by means of a barrel, introducing a fuel from an outside of the barrel into a fuel pressing chamber in a range surrounded by a tip of a plunger and the barrel, effecting pressure to the fuel by a lift of the plunger, and sending it under pressure to the injection valve mechanism. Therefore, not only the barrel but also the injection pumping mechanism and the injection valve mechanism must be firmly supported to the housing or body (called as "housing" hereinafter).
Securing structures of the barrel to the housing have been conventionally seen as follows:
(1) The housing is formed with a hole larger than the outer diameter of the barrel, inserting the barrel idly into the housing hole, directly screwing a nozzle holder from an opening of the housing hole, and pressing the barrel in an axial direction toward the bottom of the housing hole with a convex at an end of the nozzle holder.
(2) The housing is formed with a hole larger than the outer diameter of the barrel, inserting the barrel idly into the housing hole, contacting a convex at an end of the nozzle holder to an end face of the barrel, and screwing a bolt into a casing from a bolt hole defined in a flange of the nozzle holder so as to press the barrel in the axial direction.
However, in each of the above structures, the barrel is only supported by the end in the axial direction thereof, and a space is defined between an outer circumference of the barrel and an inner wall of the housing. Therefore, due to the pressure of the fuel acting on a contacting face between the nozzle holder and the end of the barrel, an oil runs out from the contacting face, and the fuel leaks outsides from a meeting between the nozzle holder and the housing, so that the pumping function is decreased and could not satisfy require of the fuel at high pressure.
A measurment therefor is to strengthen screwing of the nozzle holder or strengthen tightening of a bolt. However, the pressure is mainly received in an area of a cylindrical end in the axial direction of the barrel. The inner diameter of the barrel must not be made small in relation with the outer diameter of the plunger which composes a fuel pressing area.
For imparting mechanical strength thereto durable enough against strong pressure in the axial diameter, it is necessary that the outer diameter of the barrel is increased in thickness, so that the outer diameter of the housing is increased accordingly, since it holds the barrel therein. Therefore, the whole body of the housing becomes large in scale and heavy in weight in compay with increasing pressure of the fuel, which affects bad influences to mouting to the engine.
Another one is assumed that the housing per se is directly machined with a barrel. However, in this process, other parts than the barrel will be composed with materials excellent in abrasion resistance or tempering property, taking much time and troubles, and accordingly increasing production cost of the unit injector while decreasing production efficiency.
The present invention has been developed to solve the above mentioned problems through many studies.
It is a primary object of the invention to provide a unit injector which is easy in production, small in scale and may stand to high pressure.
For accomplishing this object, the housing is formed with a stepped hole, into which a barrel having been finishing-processed with an inlet port and an outlet port is fitted by cooling and fixed, so that the barrel is supported in the housing at not only an end portion but also the outer circumference.
In the invention, the housing is provided integrally with an injection pumping part and an injection valve part. The injection valve part is formed with an oil path extending toward a nozzle body secured coaxially therewith, and the injection pumping part is formed with a stepped insertion hole and an oil well larger than this hole in diameter. The barrel has a fuel inlet port communicating with the oil well and an outlet port communicating with the oil path, and is finishing-processed in shape and size for coinciding with the stepped insertion hole. This barrel is inserted into the stepped hole while it is shrunken in size by cooling, and when returning to the room temperature, it recovers the shrinkage to an initial size and then it is closely united with the housing at the outer circumference and the end face.
Thereby, since the supporting area of the barrel is increased, and stress is dispersed, strength of the barrel is substantially improved. The barrel is not urged into the housing at the room temperature, but the former is inserted under condition that it is shrunken by cooling. Therefore, its strength is sufficient to be durable to force required to be inserted into the stepped hole. So, the barrel may be made thin in thickness, and the housing may be made small in diameter. In addition, the injection pumping part and the injection valve part are integrally united with the housing, and any connecting part of members does not exist, and the barrel is integral with the housing at high precision and so durable to the high pressure. The fuel does not run out from the contact therebetween, and pressure in a chamber can be fully heightened.
It is another object of the invention to provide a unit injector which may return the fuel effected with high pressure is exactly returned to low pressure without leaking outside for sending under pressure.
For accomplishing this object, the stepped insertion hole is formed with a plug hole having a female screw in an axial direction thereof, and a plug is inserted into the plug hole to form a high pressure sealing part as well as a slit communicating with the oil well in the housing, said plug having an edge contacting to the end of the barrel.
It is a further object of the invention to provide a unit injector which can exactly and automatically withdraw the air entering within the housing when the device is set up, or staying together with the fuel, so that exactness of performance test of the device can be assured after setting up, and improve starting capacity of an engine.
For accomplishing this object, the invention removes a dead zone of a fuel pressing chamber upper than the outlet port. A seat is formed at an opening of a plunge sliding hole formed in the barrel, and the plug is incorporated with a check valve seating on said seat. The the fuel is pressed, the check valve is opened by this pressure, and the fuel is sent under pressure to the oil path via the outlet port bent at the top of the barrel inner than the edge part.